Regulation of transmission



March 2 1926;

D. K. GANNETT REGULATION `OF TRANSMI SS I ON `Filed Nov. 24, 1923 2 Sheets-Sheet l lilil 0m I I\u nn p L .j WL HASH/.f1 Q .M f l l 3 M f M A u /f/U I IIIIIIIIIIII :1

y INVENTOR 6am/fifi A TTORNE Y Mmh 2 1926. 1,574,808

D. K. @ANNI-:TT`

REGULATION OF TRANSMISSION Filed Nov. 24, 1925 2 sheets-Sheet 2 ATTORNEY Patented Mar. 2, 1926.

j UNITE PATENT oFFicE'.

DANFORTH K. GANNETT, OF JACKSON HEIGHTS, NEW YORK, ASSIGNOR -TO AMERICAN TELEPHONE AND TELEGRAPH COMPANY,'A CORPORATION 0F NEW YORK.

REGULATION F TRANSMISSION. i

Application filed November 24, 1923.' Serial No. 676,836.

To all -zezom t may concerti.'

Be it known that I. 1)Ai\non'1rr` lx. GAN- Nrz'r'r, residing at Jackson Heights, in the.

, from time to time, due to various causes, so

l that a circuitvwhich would give good transmission at one time might give an indifv ferent or even a very poor volume of transmission at another time unless some arrangements were provided to maintain the transmission substantially constant.

It isone of the objects of the present invention to provide an arrangement which may bel associated with the terminal of the transmission circuit and which will operate under cert-ain conditions in response to a change in rthe transmission conditions'o-f the line to actuate a. signal indicating abnormal transmission conditions or to automatically operate an adjusting arrangement associated with the line to adjust the transmission to its normal value.

Another object of the invention is lto provide a regulating arrangement of the type referred to which may be common to a 'plurality of lines and` Will operate under certain circuit conditions to cause an adjustment of the transmission of any one of a' large group of lines. Another object of the invention is .to provide a transmission regulator common to a'. large group of lines which `will function to control the adjustment of the transmission of any given linewhenever a voice frequency ringing current is transmitted over the line. These objects, as Well as other objects of the invention. are attained by means of the arrangements set forth 'ini the. following description and illustrated in the accompany ing dran'ing. Figures 1 and 1 of which, when placed side to side. (liscio-e a circuit arrangement embodyingr the invention and Fig. 2 of which shows curves for elueidating the principles underlying the transmission reeulator apparatus.

1:fleferring to Figs. 1 and 1a of the drawing, the ringing and other apparatus associated with a plurality 4of transmission lines is shown in Fig. 1` Transmission regulating arrangementscommonto a plurality of lines are illustrated in the lower art of I"ig. 1 While the upper part of 1`ig. 1a illustrates the transmission adjusting means rssociated with and individual to a single L, and L2 designate two long distance transmission lines entering an exchange 'and terminating in the usual drop arrangements (not illustrated). A voice frequency ringing arrangement is associated with each line but. since this feature is thesame for all of the lines involved it is only illustrated in detail in connection with the yline L, and will therefore only be described in connection with said line. Since it is customary to provide low frequency ringing apparatus at the drops the .ringer` is arranged to translate the low frequency ringing current transmittedffrom the drop to some voice frequency as,

-for example, 1,000 cycles, for transmission the drop side of the line. is tuned to the frequency of 20 cycles and includes relay 11 operating in response to ringing current from the drop to complete a circuit for a switching relay 12 associated with the bridge 13 across the line side ofthe circuit. The relay 12, when operated, diseonnects'the bridge 13 from the line and applies a ringing frequency of 1,000 cycles to the line, said ringing frequency being transmitted at a group frequency of 20 cycles per second.

The circuit 13 has associated therewith a tuned circuit 14, said tuned circuit being resonant at the ringing frequency of 1.000 cycles so that the incoming ringing frequency from the line will be transmitted to a. detector DI, schematically illustrated in the drawing. This detector may be of any welliknon'n type, suf-h as a vacuum tube, detector. and functions to translate the received ringing current havinga frequency of 1,000 cycles and transmitted at a group frequency of 20 cycles pery second intoY a pulsating current of' the latter frequency. The pulsating current operates a relay 15 in the output circuit of the detector to controlthe circuit of a, switching' relay 16, said switching relay functioning to 'disconnect the tuned circuit from the drop side of the line and apply 20v cycle ringing current to the drop'. V t

The ringing arrangements above described are merely typical of the general type of circuit arrangement employed in connection with voice frequency ringing and' are not to be understoodv as showing the best practce'in this connection, the details of this portion of the circuit constitutingno part of thev resent invention.

the line 1 andare operated over sleeve connections from the ringer arrangement'. The relay 17 is operated whenever 20 cycle ringing current is.' vtransmitted from the drop or 1,000 cycle/ringing current is received lfrom the lineto disconnect the line from the drop. The relay 18 is operated over a sleeve connection from the ringer only in response to ringing current of 1,000 cycles received from the line. Under the latter conditions relays 17 and 18 are both actuated to establish a connection throu h resistance R1, to conductors 1 and 2. y means of a suitable switching arrangement S, conductors 1 and v2 may be connectedito either of two regulating arragements X-and Y. These regulatingarrangments are common to ally of the lines of alarge group,

of which lines L, andA L2 are t pical. The

arrangement X is used'when t ie transmission regulator is only intendedfto actuate a signal indicating an abnormal transmission condition. The arrangement sho-wn at Y, on the other hand, is used when it is dcsired to automatically 'adjust the transmission of any given line.

By means of the switch S, alreadyk referred to, control conductors 3 and 4 associated with the transmission regulator Y may be connected to conductors `3 and 4 These conductors 3 and 4' are extended successively over contacts controlled by relays similar to relay 18, associated with all or' the lines of the group, rand when any rclay corresponding to 18 is operated said relay functions to connect the conductors 3 and 4. to the automatic transmission adjustingdevice associated with'that line, as will be described hereinafter. This operation takes place at the same time that they transmission regulator is associated wi-th the line over conductors 1 and 2. The switch Sinay also be so adjusted as to connect the control conductor i" of the transmission regulator 'X to the conductor 4. 1When the arrangement X is 'to be used vthe switch S, associated with thel line will be thrown to con- 'with respect to the filament.

nect the conductor 4 to the signal lamp 20 associated with the line, the switch S, at the same time disconnecting the conductors 3 and 4 from the transmission adjusting ai'- rangement, to be described hereinafter. The conductors 1 and 2 leading to the transmission regulator X or Y, as the case may be, are also connected serially over the contacts of relays similar to the relay 18 associated with each of the lines so that any line may be connected by its relay 18 to the transmission regulator whenever a voice frequency ringing signal is received by that line, provided a line whose relay contacts are included in the connection nearer the ltransmission regulator is not at the same -tnne receiving a ringing signal. Two relays, 17 an 18, are associated with l Coming now to the transmission regulator itself, which may be common to a plurality of Alines and maybe connected tol any line o'f the group when a ringing signalis reccived over said line, it will be seen that the regulators X and Y are somewhat similar. Each regulator includes an incoming circuit as illustrated at 21 and 22tuned to the ringing frequency of 1,000 cycles. Each regulator also includes an am lliiier, as shown at A and A', as Well as a up`.ex de# tector arrangement illustrated at vD and D.

The circuit arrangement of the detector is a vital feature of the regulator and will be described in some detail. A description of the detector arrangement D will be suiiicient for this purpose. This detector comprises 'two vacuum tubes 23 and 24, ofthe usual type. The input circuit of each tube contains a Very large resistance, for example, a resistance of two megohms. A C battery common to the input circuits of the two tubes is provided and the connections are such that the normal grid potentials of the two tubes are different, the grid of the tube 23 being connected to a point on the C battery which is nefrative by an amount e1 with respect to the filament while the circuit of the grid ofthe tube 24 is connected to a point which is negative by an amount e2 l The `voltages e, and e2 are bothlarge compared with the grid voltage required to reduce the space currents in the two tubes approximately to zero. The two input circuits are connected' to the output circuit of the amplifier A through separate windings of a common transformer and the output circuit of each of the Vdetector tubes is tuned to the group frifequ'ency'o'fv 20 cycles.

The operating characteristics of the tubes are illustrated 4by the curves of Fig. 2. As has already been stated, the ringing current which is received from the line and impressed upon the detector of thc transmission regulator consists of current having a frequency of 1,000 cycles and interrupted at va group frequency of 20 cycles per second. The output of the detector tubes,

therefore, is a pulsating current having a frequency of 2O cycles per second and is used to operate the relay arrangements of the regulator, to be described hereinafter. The characteristic curves of the two tubes,

therefore, show the cycle output of the vrange of the tube.` For all small values ofV A. C. potentials applied to the grids of the tubes, which potentials are not large enough in magnitude to reduce the negative grid potential at any point in the wave to a.

value suiiicient to permit space currentfto flow in the plate circuit of the tube, it

f so

put amplitude.

, obvious that no 20 cycle output current will flow. For A. C. voltages whose peak values exceed the negative C potential 1 or 62. of the grid battery so that theY grid potential tends to become positive, it is ob- Avious'that the grid to filament impedance of the tube 23 or 24 will become quite small4 comparedwith the two megohm resistance potential is eil'ectively revented from bei coming appreciably positive even'for very large values of applied A. C voltage` The` eiiect of this is to cause the curve to dro oi sharply` and become flat so that this part of the curve is almost horizontal, as shown. In other words, the C potential being so adjusted that no current iiows in 'the' output circuit, normally, the A. C. current current to flow in the output -circuit until the amplitude is increased to a limiting value, A' depending upon the4 .normali potential. ,When this point is reached and' the amplitude is further increased an out-5v putv current begins., to flow, 'this output i reaching a i maximum lfor a `very lsmall further increase ,in amplitude, and'noj'sub-'fA stantial increase inA the output currentoe--l lin the' 'out- "v curs for still further increase Since the two of received current at which they give suicient 20 cyclev'output to. operate relaysor other devices in their respective circuits-are diii'erent.

regulator Y, each. detector tube has a separate polar relay associated with its output circuit; for example, a polar relay 25 is associated with the `output circuit -of the detector 23 and a polar relay'26 is associated with the output circuit of the 'detector 24, each of these polar relays being respon- Vn., both polar'relays operate. i

The vibration of the armaturesof these n tubes" are provided with, different grid potentials the critical values,

In the case of the transmission current appears in the lower.

lsire to 20 cycle current. lVhen the value' of the received 1,000 cycle current lies between zero and m 4(see Fig, .2) neither polarl value of the .received current is greater than When Vthe 75. 'A

relays is lmade-to control the operation-of alternating current relays 27 and 28 by switchlng connections from a battery 'so that current iiows through the relaywinding irst in one direction and then the other,I

as the armature vibrates, The contactscontrolled. by the relays 2,7 and 28 are so:

arranged that if. both relays operate a" ground 1s connected to the control circuit 3 connected to the'contro 'circuit 4.. I- but If neither relay o crates a ground is onerelay operates, or, in other words, ifV

onlyl the relay 27 operates, `ground -is connectedP to neither of the control conductors. This last mentioned condition corresponds tothe condition wherein the received 1,00()

-cycle ringing current has an .amplitude llying between the points 'mand n in Fig. 2. connected in series with the grid, during. portions of the cycle. Therefore, the grid ofthe transmission is made. If the ampli- '100 tudedrops below m, however, or goes above 01 .the transmission of the circuit will be adjusted in the manner hereinafter to'be described to bring the transmission back `within the normallimits.

The arrangement controlled by the detector 1) of the regulatingl arrangement X is similar to Athat described in connection vwithitheregulating arrangement Y except that :in this case 'a single polar relay 29 is 4differentially connected to the output circuits of 'the two detector tubes and operates *aA single A.l C. relay 30, which determines ,whether or not ground `will 'be appliedto 'the control circuit 4,7. The vibrating polar ."relay 29 does not operatewhen the received v1,000 cycle current. has an yamplitude less than fm. or greater thanffn, for in the. former l case the amplitude lis too -small to produce ",{any output currentV inv either tube while in 4the latter case theoutputcurrents are of.

substantially the' same amplitude and oposeyeach other. When the received ringing current has an amplitude lying between 11o. Jl

the limits m and n., however, a detected current of 2O cycles appears in the output circuit of the upper tube while no detected lonsequcntly, the polar relay 29 vibrates its armature at 20 cycles per second and operates the A. C.

Cfr

relay 30. The latter disconnects ground from the control circuit. 4, thereby preventing the operation ot." the signal lamp, such as 20, associa-ted with the transmission line. 'hen the received transmission is either above or below the limits m and '11, the relay 30 is not operated and the conductor 4' is grounde-.l so that the signal lamp is actuated.

At the upper part of Fig. 1" is illustrated the transmission adjusting arrangement associated with the line L, when the automatie transmission. regulator Y is to be used instead ot the signal (.-mltrolling regulator X. lt will be. understood vthat a similar transmission adjuster will beassociated with each line ot' the group. As already stated, the automatic regulator connects ground to either one or thc other of the control circuits 3 or el. if the circuit equivalent of the line at the time of the transmission of ringing current is outside the specified limits. These two control circuits are associated with the. transmission adjuster and the latter is arranged to change the equivalent of the. circuit by a given amount, each time the regulator operates. The equivalent-is increased or decreased, depending upon whether the control circuit 3 or 4 1s grounded.

The transmission adjuster consists of a group ot' relays called control relays which may be of any number to produce the de` sired number of 'steps of adjustment. These relays are shown as four in number and designated a', b', c and d and another group of relays called operating relays and designated a, b, c and d. The operatlng relays are controlled by the control relays and the operation of the control relays is in turn determined by relays 31 and 32, included in the control circuits 3 and f1 respectively.

lhe contacts of the operating relays are arranged to adjust by steps an H type of artificial line or pad, H, in the line L,. This artificial line comprises series resistance-s in each line Wire and a shunt resistance connected to the midpoints of the series resistances. The contacts are arranged to adjust by steps the series resistance elements on eachside of the midpointand to simultaneously' adjust the shunt resistance, thereby changing the transmission loss but not the impedance characteristics of the line. Ilhc control relays are so arranged that when a given relay with its corresponding operating relay is operated and the artificial line H given a particular adjustment, a `ground placed upon the wire 3 will operate the control relay to the right of the conti-olf relay then operated and when the 'ground is removed at the end of the ringing signal the preceding relay will be rcleased.l On the other hand, it ground is -clear from a description o placed on the wire 'l the relay to the left will be operated and when the ground is rcmoved at the end of the ringing signal the original relay will be released. .Each ringing signal serves to adjust the network H one step, if any adjustment is required. When the limit of adjustn'icntis exceeded in either direction the relay Z, or Z2 will be operated to close a circuit of the signal lamp s, or s2, which will be locked up until the abnormal condition is overcome, when the relay Z, or Z2 controlling the lamp may be released by means of a suitable key, K, or K2.

Further details of the ap aratus will be the operationv which is as follows: It' 20 cycle -ringing current is transmitted from the drop terminal of the line L for example, the ringing current will flow into the tuned bridge 10 and operate the relay 11, which in turn closes a circuit of relay 12. 'lhe relay 12 opens the tuned bridge 13 and applies 1,000 cycle ringing current, interrupted at a group frequency of 20 cycles per second, to the tip and ring conductors of the line 1.1,. The operation of the relay 12 also applies ground to the sleeve conductor of the ringer so that a circuit is completed through a resistance and through the Winding of the relay 17. The relay 17 is actuated to disconnect the conductors of the line L, from the drop terminals during the ringing operation but as the relay 18 is not actuated the transmission regulator does not come into play.

When 1,000 cycle ringing current, vinterrupted at a group frequency of 20 per second, is received from the line L however, the ringing current is transmitted through the bridge 13 to the tuned circuit 14. The

detector'D, detects the ringing'current producing a pulsating frequency of Q0 cycles per second, which actuates the relay 15 to close the circuit of the relay 16. The relay 16 opens the tuned circuit 10 and connects 20 cycle ringing current to the tip and ring conductors of the drop terminals. same time the relay 1G connects ground to the left-hand sleeve conductor of the ringing arrangement, thereby completing a circuit through the windings of relays 18 and 17 in series. Relay 17, as before, disconnects the drop terminals from the line conductors of the line L, and connects the line L1 through the resistances R, and over the make contacts of the relay 18 to the conductors 1 and 2.

Assume now, that the switch S is in the position shown in the drawing, so that the conductors 1 and 2 are connected to the transmission regulator X and that the switch S, of the line L, isin its upper position so that the signal lamp 20 will be employed rather than the transmission adjuster. The ringing current incoming from At the l 25 detected current in the output circuits of the the line Llwill be transmitted over the conductors l and 2 to the tuned circuit 21 and will be amplified by the amplifier A1 and impressed upon the detector arrangement D1. If the transmission equivalent of the line L1 is normal so that the amplitude of the received ringing current lies within the range @1i-11 (see Fig. 2) substantially no 20 cycle current will bedetected in the output circuit of the lower tube of the detector D. The upper tube, onthe other hand, will det'ect a' 20 cycle current which will be transmitted to the vibrating relay 29 to cause its armature t6 vibrate.V armature of the relay 29 will operatethe alternating current relay. 30 to disconnect ground from the conductor 4".

.. quently, no circuit lwillflo'e completed forthe .ceived' 1,000 yeycleffcu'r lies'- ductor 4.

below m, the relay`v2i9f-wijllsaio bejactuated In the former casethis willbefbecause the two tubes will be substantiallyr'lequal and will balance each othefrwhile 1n the llatter case substantially no currentvifillbetdetectedl in the output circuit ofeither' tube. -As a consequence, the relay*30"-will n-otbe operated and ground will 'be applied' to the con- Current Will'new rflow through the highresistance winding vof relayf33. By

vreason of the high resistance of the Winding of the relay 33 the current fiow'ing'over the conductor 4 and the conductor 4 is insuiiicienttto energize the relay 3G andthe signal lamp 20. After anl instant, however, the slow operating relay 33 attracts its armature and .shunts IitsI high resistance vwinding by a low resistance winding, thereby increasing the current iiow lover the conductors 4' and 4. The current flowing over the-circuit .4 is now sufficient to cause the lamp 20 to gloW and to energize the relay 26,j which closes a locking circuit through -its winding and through the lamp 20v to hold the lamp 20 energized after the circuit has-been opened by the release of therelay 18jat the end'of the ringing signal. The lamp indicates'to an attendant that the transmission-is abnormal and the attendant`can the adjust the transmission to aA desired value in anyjwell known manner. j y j lf 1,000 cycle ringing current .should be received from the line L2 the"1j`elays=assoi ated with said line correspondingto the. re-

lays 17 and 18 of theA lineLl w`illbeactu ated to connect the conductors 1 and2 to- -from the line L1 lan however, the; transmissioncondition. of thelinelfLi'is -abnormaliveitlier too high on .if the r'e d le or taneously the' line nearest the transmission regulator obtains dprecedence and will have its transmission a justment signal operated.

If, when the ringin current was received its relays 17 and 18 4were operated,.the switch S should be in its alternative position, indicated in dotted lines, and the switches Sl'and S2 associated with the individual lines in their lower positions, the transmission regulator Y will come into play and the automatic transmission adjuster will be operated. In this case the 1,000 cycle interrupted ringing currentl received from the line will be transmitted over the contacts of the relay 17 through the resistances Rl and over the upper contacts of relay 18 and conductors 1 and 2 to thel tuned circuit 22. The ringing current will then bey ampliiedby the ampliiierA and impressed upon the detector D.'

If the vtransmission is normal, so that the amplitude of the received ringing current lies within the limits m and n of the curve of Fig. 2, 20 cycle current will be produced in the output circuit of the tube 23 but no detected current will appear in the output circuit of the tube 24; Consequently, the vibrating relay 25 will be energized so that its' armature will vibrate and actuate the alternating current relay 27. The relay 27 willattraet its armature to disconnect the Ground normally connected through the high resistance I Winding of the relay 34 to the conductor 4'. lhis produces no effect upon the transmission adjuster, shown in tion of. justment which then obtains.

If the amplitude ofV the received'1,000 i cycle current should be lower than thepoint m of Fig. 2, 20 cycle current will be detected in the output circuits of neither tube and neither of the relays 27 nor 28 will be operated. Consequently, a circuit is complet-ed from -ground through the high resistance lio winding of the relay 34, over the back con- Vftthis current is not sulicient to operate the relay 32 but when the relay 34, after an instant, attracts its armature and shunts its high resistance winding by its low-resistance winding, the current is suiiciently increased to energize the relay 32.

Assume, now, that the circuit of the transmission adjuster is in the condition shown, with the relays b and b actuated. The energization of the relay 32 will com )lete a circuit from battery, over the upper ront contact of said relay, `lower back contacts of relays d and c. lower front ot relay b and-throughthe winding of the relay a' to ground. The relay a is accordingly energized and is locked up over its inner lower front contact to battery. A circuit is also completed over its inner lowor front Contact for the winding of the operating relay a, which by closing the a contacts of the network H, short circuits the entire network and produces the maximum transmission adjustment for the line L,. y

At the end of the ringing signal the relays 17 and 18 will be released and the circuit over the conductor 4 to the relay 32 will be opened. lVhen the relay 32 releases its armatures its lower contacts close to connect ground, over the upper'backl contact of relay 31, upper front contact of relay a Vto the winding of the relay b', thereby short-cireuiting the winding of said relay and causing it to release its armatures. The opening of the inner contacts of relay b disconnects the battery from the operating relay b releasing it.l The relays a and a will now remain energized, with the transmission adjusted as indicated, until a subsequent ringing signal is received.

In case the amplitude of the received ringing current from the line L, had exceeded Vn, of the curve of Fig, 2, 20 cycle current would have been detected in the output circuits of the tubcs23 and 24 so that both relays 27 and"28 would he energized. A circuit would then be completed from ground, over thef'front contacts ot relays 27 and 28, over conductor 3', over conductor 3, inner front contact of relay 18, upper bar ofl switch S, and through the winding of relay 31 to battery. Assuming that the 'circuit of the transmission adjuster is at this time in the condition shown in the drawing, with relays b and b energized, a

circuit will be completed from battery, over i the upper front contact of relay 31, upper back contact of relay a and over the upper'front contact of relay b. through the winding of relay o to ground. Relay c', upon being energized, is locked up and completes a circuit yover its inner front contact for the operating relay o. Relay 0 closes the contacts designated c in the network H, thereby increasing the series resistance elements ot the network and decreasing the shunt resistance elements. This produces a corresponding increase ot the transmission loss of the line 1.,.

At the end of the ringing signal the relays 27 and 28 will release their armatures and the relays 17 and 18 will be released so that the circuit over conductor 8 will be opened and the relay 81 deenergized. lVhen the armature of said relay falls ofi' its lower contact is closed to connect ground, over the upper back contact of relay 32, over the lower back contact ot relay d and over the lower front contact of the relay c to the winding of relayb. The winding of the relayb is accordingly short circuited and the relay is deenergized and restored to normal, thereby opening the circuit of the relay b, which i's likewise deenergized. The network H now .remains in the condition of adjustment to which it is set by the operation of .the relay c until a subsequent ringing signal is received.

It will beobserved that under the conditions in which neither'relay 27 nor 28 was operated the high resistance winding of the relay 34 was momentarily connected in circuit with the relay 32, thereby slightly delaying the operation of the latter relay. This was for the purpose of preventing a false operation of the transmission adjuster in case there should be a slight delay in lthe energization of either the relay 27 or 28 or both. The relay 33, it will be re called, was also included in circuit with the conductor 4 fork a similar reason, viz, that too slight a delay in the operation of the relay 8O migxht result in energizing and locking upt e lamp 20, even though the transmission lconditions be normal.

If, when a ringing signal is received, the transmission adjuster is set for the condition of maximum transmission with relays a', and a actuated, and the amplitude of the ringing current should be lower than m of `Fig. 2, the conductor 4 will be grounded in the manner already described, thereby causing the relay 32 to be energized. Battery will then be connected over the upper front contact of the relay 32 and over the lower back contacts of relays df', c and b and the-nce over the lower front contact of relay a to the winding of relay- Z,. The latter relay will then be energized and locked up over its lower front contact, completing a circuit through the signal lamp 8 which indicates that the transmission conditions of the circuit are so abnormal as to exceed the limits of the transmission adjuster. The relay l, is provided with no upper Contact and consequently when the relay 32 falls off at the end of theringing signal no momentary impulse is transmitted to -short circuit the relay a and the latter relay. still remains operated. l/Vhen the attendant has made a suitable change in the transmission of the line circuit the key K, may be actuated to release the relay Z, and the lamp 8,.. The transmission adjuster will, however, remain with the relays a and a energized after the key K, has been actuated.

It on the other hand, the transmission adjuster hadbeen so set that the relays d and d were actuated, and the amplitude of the received ringing current should be greater than n, so that both relays 27 and 28 are energized, the conductor 3 will be grounded to complete a circuit for the relay 81. Battery would then be connected over the upper front Contact of relay 3l, upper j back contacts of rela s ci', b and o and upper front Contact ot relay al to the winding of the relay Z. The relay Z2 would then be energized and locked up over a circuit including the signal lamp s2 so that an abnormal adjustment ht the circuit would be indicated. Iu this instance, also, the relay Z would not be short circuited at the end of the ringing signal and after the attendant has made suitable transmission changes the relay Z.2 could be released by means of the key IQ. leaving the transmission adjuster set with the relays d and [l energized.

It will be observed from the circuit arrangement slioivn in Fig. l that a single transmission regulator Y or X, as the case may be, will serve a large group ot lines, the regulator being automatically connected to any given line Whenever a ringis received on that line, provided always that a ring is not being simultaneously received on an' other line nearer the regulator. It is appar-ent from the arrangement of the circuits that the line L which is the line nearest the regulator, will receive the most frequent regulation and a line further away from the regulator will receive regulation only when lines between it and the regulator are not signaling. However', iii practice it is found that only about one per cent of the time of a circuit is occupied by signaling, even at the busy hour. Consequently it follows from the laiv of probability that it the group served b v the regulator contained 100 circuits the circuit furthest from the regulator would still receive iegulation-onl the average about one time out of three. It the group contained only 10 circuits the circuit furthest from the regulator would receive regulation 90 per cent of the time. It is apparent, therefore, that the group of lines served by asingle regulator may be made quite large.

An important advantage of the invention resides in the fact that the functioning ot the detector arrangen'ient of the regulator is very nearly independent of the characteristics ot the tubes but is determined principally by the adjustment of the grid potentials e, and e2. It is, therefore, necessary only to maintain the adjustments of the grid batteries ivitliin fairly close limits. It

is not necessary that the batteries supplying the filament and plate currents should be carefully adjusted. It will, of course,l be necessary for proper operation of the arrangement to maintain the voltage of the 1.000 cycle ringing generator which supplies the ringing current at the transmitting end ot the circuit within rather narrow limits. This may readily be done, however,l by various arrangements Well-known in the art.

Another important feature of the invention is the use ot the iesistances. such as It, and liz, in the connection between any given line and the transmission regulator. The group of lines with which the transmission regu ator is associated may consist ot lines lwhich, because they are of different lengths or for other reasons, are operated at diterent normal transmission equivalents. In Orderto make possible the use of -a single transmission regulator having one adjustment with all the lines of the group, it is necessary to equalize the losses ot the lines to the regulator byinserting additional losses in series between the lines and the regulator, these additional losses being larger for the lines of lowest loss, and smaller for the lines oi greatest' loss. The resistances R1 and R2, etc., serve as these additional Vequalizing losses.

It Will be obvious that the general principles herein disclosed maybe embodied in many other organizations Widely different from those illustrated Without departing from the. spirit of the invention as defined in the following claims.

lVhat is claimed is:

1. In a signaling system, a plurality 'ot transmission lines, a transmission responsive device common to said lines and responsive to changes in the transmission equivalent ot a line when connected thereto, means to connect said device with any one ot said lines and means associated ivitlisai-d trans-` mission responsive device fer producing an indication in response to an abnormal trans-` mission condition ofl a line to which the transmission responsive device'is connected.

9.'. In asignaling system, transmission lines, a transmission responsive device common to saidlines and responsive to changes in the transmission equivalent of a line when connected thereto, means to connect said transmission responsive device to any one of said lines in response to the transmission ot a signal over said line and means controlled by said transmission'responsive device to produce an. indication in` response to an abnormal transmission condition ot a linev to which the transmission responsive device is connected.

3. In a signaling system, a `plurality of transmission lines, a transmission responsivel device common toA said lines, means to connect said transmission responsive device to any one of vsaid lines upon the transmission of ringing current over said line and means controlled by said'transmission responsive device for producingan indication in response to -an abnormal transmission con;l dition of the line to which said transmission responsive device is connected;

4. In a signaling system, a plurality ot transmission lines. a transmission responsive device commonV thereto, means to lconnect said transmission responsive device to any one of said lines in response to a voice irequeniv ringing current transmitted over said a plurality ot line and means controlled by said transmission responsive device for rproducing an indication in response to yan abnormal transmission condition `of the line to which said transmission responsive device is connected.`

In a signaling system, a plurality of transmission lines, a transmission adjuster for each line, atransmission -responsiveqdevice common to vsaid lines, means to connect said transmission responsive device to any one of said `lines and means controlled by` said transmission responsive device `in respense to an abnormal transmission condition of a line to which lsaid transmission responsivel device is connected to operate the transmission r,adjuster for said .line

6. In a signaling system, a plurality of transmission lines, -a transmission adjuster for each line, a transmission responsive device common to said lines, means to connect said-signal responsive device -to any one of the lines in response to a signal transmitted over said line vand means controlled kby said transmission responsive device in response j to an vabnormal transmission condition of a line to which said transmission responsive device is connected to operatethetransmission adjuster for said line. l v

, 7. In a signaling system, a plurality of transmission lines, a transmission adjuster foreach line, a transmission responsive device common to said lines, means to connect said transmission responsive device'to any one of said lines in response to ringing current transmitted over said line and means controlled by. said transmission responsive device vin response tto an yabnormal transmission'eoi'idition of a line to which said transmission -responsive device is connected rto operate the transmission adjuster for said line.

8. In a signaling system, a plurality of transmissie?, lines, a transmission adjuster for eachlli'ne, a transmission responsive device common to said lines, 4means to ,connect said transmission responsive device to any oneof said lines upon the transmission ofa voice frequency ringing current over saidy device common to said lines, means to con-p neet said transmission responsive device to any one ot' said lines inresponse to the transmissionof signaling current over said line, ineaiisl to impress said signaling current upon said transmission responsive device and means controlled by said transmission responsive device to produce an indication ivlien said signaling current arrives at said transmission responsive' device with abnormal amplitude.

10. Ina' signaling system, a plurality ot'` signaling' current over said line, means to impress said signaling ycurrent upon said transmission responsive `device andfmeans controlled by'said transmission responsive ,device to operate the transmission adjuster 'for the line when said signaling current arrives atfsaid transmission vresponsive device Witli'abnormal amplitude'.

l1. Inasignalingsystem, a plurality of transmission lines,fand'-a transmission adjuster for each line, said'transmission adjuster comprising a variable impedance element associated with the line and a series ofcounting relays forcontrol-ling the settingI ofsaid .impedance element, a transmission responsive device coiiimon to said lines, means to connect said `device to any one of said l-ines in response to the transmission oi"l a signaling current thereover and means controlled by said transmission responsive device When the transmission condition of the line to which it is connected is abormal to operate the counting relay adjacent a previously operated counting relay of the transmission adjuster associated with said line', thereby producing a different setting of said impedance element.

12. In a signaling system, a plurality of transmission lines, a transmission adjuster for each line, said transmission adjuster comprising va variable impedance' device associated with the line, a plurality of counting relays for controlling the setting of said impedancede'vice, said counting relays being so arranged that when a given relay is operated it Will set and maintain the setting of said impedance device until another counting relay is operated, a transmission responsive device common to said lines, means to connect said transmission responsive device to any one of said lines in response to the transmission of a signaling Vcurrent thereover and means controlled by saidl transmission responsive device when said4 device is connected to a given Atransmission line .to produce no effect upon said transmission adjuster when the signalingl current arrives at said transmission respon- 'siveA device with normal amplitude, said means operating wlientlie amplitude of the signaling current exceeds the normal limitto'operate a counting relay on one'side vof thecountiiig relay then operated to increase the loss ot' said impedance `device and said means operating when the amplitude of the signaling current is below normal4 to actuate the relay on the other side of the counting relay then actuated to decrease the impedance of said impedance device.

13. In a signaling system, a plurality of transmission lines, a transmission adjuster associated with each line, said transmission adjuster comprising a variable impedance device associated with said line and means to vary the loss of said device by steps,sig naling means associated with said last mentioned means adapted to be operated when said last mentioned means is adjusted above or below the limits of said impedance device, a transmission responsive device common to cach of said lines, means to connect said transmission responsive device to any one of said lines upon the transmission of a signaling current thereover and means controlled by said transmission responsive device to operate the transmission adjuster of the line with which it is associated whenever".

a signaling current arrives at the transmission responsive device with abnormal amplitude. j

1-1. In a signaling system, a transmission line, a transmission responsive device to which alternating signaling currents may be transmitted over said line, said transmis-l sion responsive device comprising a'pair of translating elements, both translating elements being substantially unaffected by received alternating currents of small amplitiide, one of said translating elements becoming responsive to alternating signaling currents above one amplitude and the other being responsive to alternating signaling currents above another amplitude.

15. In a signaling system, a transmission line, a transmission responsive device to which signaling currents may be transmitted over said line, said transmission responsive device comprising a pair of translating elements, both translating elements being substantially unaffected by received currents of small amplitude, one of said translating elements becoming responsive to signaling currents above one amplitude and the other being responsive to signaling currents above another amplitude,

and means associated With vsaid translating elements for producing an indication when neither of said elements responds, said means producing no indication when only one of said elements responds andl said means producing an indication when both of said elements respond.l

16. In a signaling system,la transmission line, a transmission responsive device associated with said line, said device comprising a pair of vacuum tubes liavinginput and output circuits, means to a ply normal potentials to the gridscf sai tubes4 such that one of said tubes is unresponsive to currents having an'amplitude below a given limit and responsive -to currents having amplitudes greater than said limit, the other tube being unresponsive to currents having amplitudes below a higher limit and being responsive to currents having an amplitude greater than said higher limit.

17. In a signaling system, a transmission line, a transmission device associated with said line, said device comprising a pair of vacuum tubes having input and output circuits, said tubes being so adjusted that their operating range is small as compared with 'the amplitude of signaling currents transmitted over said line, means to apply normal potentials to the grids of said tubes such that one of said tubes is unresponsive to currents having an amplitude below a given limit and responsive to currents having amplitudes greater than said limit, the other tube being unresponsive to currents having amplitudes below a higher limit and being responsive to currents having an amplitude greater than said higher limit, and

means controlled by said-tube, said means producing an indication',- when vneither of said tubes is responsive` to signaling currents, said meansproducingvno indication when but one of said tubes is responsive and said means producing` an indication when' both 'of said tubes are responsive.

18. -In asignaling system', a plurality of transmission lines, a transmission responsive device common to said lines, means to connect said transmission responsive device to any one of'said lines upon the transmission of signaling current thereover,v said transmission responsive device comprising a ssl pair of translating elements, both translating elements being substantially unaiteeted by received currents of small amplitude, one

of said translating elements becoming responsive to signaling currents 'above oneI amplitude and the other being responsive to signaling currents above another amplitude. 19, In a signaling system, a plurality of transmission lines, a transmission responsive device common to said lines, means to connect said transmission responsive device to any one of said lines upon the transmission of signaling current thereover, said transmission res onsive device comprising a pairof translating elements, both translating elements being substantially unaffected by received currents of small amplitude, one of said translating elements becoming responsive 'to signaling currents above one amplitude and the other being responsive to signaling currents above a certain amplitude and means associated with said translating elements for producing an indication when neither of said .elements is affected, said means producing no indication when only one of said elements is devicecommon to said lines, means to co'n-A 'Y neet said transmission responsive 'device vto any one of said lines upon the transmission of signaling currents thereover, said device" comprising a pair of vacuum tubes having Iinput and output circuits, said tubes-being so adjusted that their operating range is small as coniparedfwvith the amplitude ot signaling currents transmitted over said'f line, means to apply normal potentials to the grids of said tubes suoli that one of said tubes is unresponsive to currents'having an amplitude below a given limit and responv sive to currents having amplitudes' greater than said limit,` the other tube being mire-- sponsive'to currents having amplitudes 'beloT a higher limit and being responsive to currents having an amplitude greater than f said higher limit. 1

21. In a signaling system. a plurality-ot transmission lines, a transmission responsive device common to -said lines, means' to con-A nect said transmission responsive devicev to any one of said lines upon the transmission of signaling.; currents thereovei'. said device comprising a pairV ofvaeuum tubes having input and output circuits, said tubes being so adjusted that their operating range is small as compared with the amplitudeo signaling currents transmitted over said line,- m'eans to apply normal potentials vto the grids of said tubes such that one of said: tubes is unresponsive to currents having an amplitude below a given limit and 'responsive to currents having amplitudes greater than said limit, the other tube being unre-` sponsive to currents having amplitudes be low a higher limitv and being responsive to currents having an amplitude greater than' said higher limit, and means controlled'by saidtube, said: means producing anV indication when neither of said tubes is respon# sive to signalingl currents, said me; .is producing no indication When but one of said tubes is responsive and said means producing an indication Whenboth of said tubes are responsive. v f

22. 'In a signaling system, a plurality of transmissionr lines, a transmission adjusterv for each line; a transmission responsive de- Vice common to said lin-es, means to'con'nect said device with any one of said linesviiponj the transmission of signaling currents thereover, said device comprising a pair of *translating elements, both translating eleiiieiitsnbeing substantially unaffected by re- .ceived currents of vsmall, amplitude, one of 'said translating.element-s becoming responsive to signaling currents Labove one amplitiide andthe other being responsive to sig- 'naliiig eur-rents above 1 another amplitude,

and means controlled by said elements whereby Whei'i-..neither of said elements responds said transmission adjuster will be o perateil in onel direction, whereby when "both ofsaid elements respond said transmis -sion adjuster Will be operated in the other 1 direction and whereby when but one `of said elements respoiid's'no leffect will Ibe produced 'upon said transmissionfadjuster;

transmission' lines; 'al transmissionadjuster for each line, a transmission responsive device common to-.said lines, means to connectJ 'said device .toany one osaid lines upon the ftransmission of signaling currents thereover, said I device .comprising a .pair lot vacuumtribeshaving input and output eir- 225,-I'n ai'signaling-systemga plurality of cuits,saiil. tubes bei-ng sokadjusted that their Lope-rating"rangeis small as compared with fthe amplitude of signaling current-s trans- Viiiitted ioveisaidline, means -to apply norvmal potentials toftlie grids of said tubes such that one ,ofl said tubes is unresponsive to currents having an amplitude below a given Vlimit and responsive `to* currents having --aiiij'ilitudes greaterthan said limit, the other ltlib'e being unresponsiveto currents having amplitudes below a higher limit and being responsive to currents-having' an amplitude 'greater than said-higherlimit, and means controlled by said tubes, saidmeaiis operat` ing when neither tube responds to adjust in one direction the transmission adjuster oi thenline-connected `tof-said transmission responsive ldevice, said .means-operating when both of said tubes respond to adjust the said t'ransn'iission adjuster ofthe line in the vopposite direction and said Vmeans producing -no adjustment. of vsaidftraiasmission adjuster vv-henvonly.v one tube responds.

'In testimony'whereof, I have signed my naine to lthis specification November, 1923,

' y niiNFoR'r-H K.k GANNETT.'

this 21st day of 

